Shaft driven centrifugal vane pumps are often used for cooling of automotive engines. Water or other fluid is directed axially into the pump and exits radially into one or more volutes. The shaft is typically mechanically driven, directly or indirectly by the engine crankshaft, and therefore rotates at some speed proportional to engine speed. Pump design affects pump efficiency. An increase in pump efficiency means less power is consumed in driving the pump, and can result in improved fuel economy. Less than ideal fluid flow results in flow separation in the flow field, which reduces pump capacity and may cause unwanted pump noise due to cavitation. Cavitation occurs when local boiling of the fluid occurs due to low pressure conditions in the separation zones of the flow. As a result, vapor bubbles are created in the flow. The bubbles collapse or implode as the flow passes from a relatively low pressure region of a pump, such as a fluid inlet, to a relatively higher pressure region, such as a discharge or outlet region.
Certain impeller designs may be configured to reduce cavitation and increase pump efficiency. The geometric configuration of the impeller, including the design of the pump vanes or blades, and the shroud, may necessitate sand casting of the impeller rather than the less expensive stamping of die casting.